Method and apparatus for actively turbocharging an engine

ABSTRACT

A system and method for monitoring at least one operating parameter indicative of an operating condition of an engine and controlling a turbocharger assist device to maintain desired operating conditions of the engine equipped with a turbocharger. In one embodiment, a controller is provided to control operation of a turbocharger assist device in an engine for generating electric power when an excess of energy exists in the exhaust of the engine to subtract work from a turbocharger drive shaft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/942,221, entitled “Method and Apparatus for Actively Turbocharging anEngine”, filed Sep. 16, 2004, which is herein incorporated by reference.

BACKGROUND

The invention relates generally to diesel engines, and more specificallyto turbocharged diesel engines.

The capability of modern engines to produce more power from a givencylinder displacement has been steadily increased due to engineeringinnovation and development. Modem engines utilize higher charged airpressure provided by turbochargers to generate more power than theirprevious generation counterparts. The amount of power obtained from acylinder in an engine depends upon how much fuel is burned in it, andupon the amount of air available in the cylinder. Therefore, byproviding more air into the cylinder the power generated is increased.Turbocharging is a technique used to increase the amount of airintroduced into each cylinder, typically by a positive pressure thatexceeds the then reigning pressure in the cylinder. Exhaust gas from theengine typically drives the turbocharger. This gas drives a turbine,which, in turn, drives a compressor to drive the additional air into thecylinder.

Conventional diesel engines used in vehicles, such as diesel electriclocomotives are difficult to start at low ambient temperatures. In someengines, the compression ratio and cranking speed are insufficient toprovide adequate in-cylinder temperature and pressure for auto ignitionof the diesel fuel. One of the ways this issue has been addressed is touse auxiliary power units to circulate hot fluids through the engine forenhanced cold start capability.

Certain transients or off-design operation can lead to turbochargersurge, which is damaging to the turbo machinery and associated hardware.Locomotives currently have few or no controls or hardware to avoid suchdamage.

To address the surge issue, turbocharged trucks and automobiles aretypically equipped with waste gate systems to limit turbocharger speed.Alternately, “safe gates” or blow off valves on the compressor dischargehave been used to prevent surge. Typically, compressor surge margin canbe improved through aerodynamic modifications to the compressor anddiffuser, but these often result in loss of compressor efficiency.

There is a need, therefore, for an improved technique for cold-startperformance of diesel engines, to prevent turbocharger surge, and tocontrol turbocharger speed independent of engine operation. There alsoexists a need for a technique to increase the engine performance toaddress the drawbacks in heretofore known systems.

BRIEF DESCRIPTION

In certain embodiments, a system and method is provided for monitoringat least one operating parameter indicative of an operating condition ofan engine and controlling a turbocharger assist device to maintaindesired operating conditions of the engine equipped with a turbocharger.In one embodiment, a controller is provided to control operation of aturbocharger assist device in an engine for generating electric powerwhen an excess of energy exists in the exhaust of the engine to subtractwork from a turbocharger drive shaft.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical view illustrating exemplary functionalcomponents of a turbocharger in accordance with aspects of the presenttechnique;

FIG. 2 is a schematic illustration of a control circuit for operating aturbocharger for a diesel engine, incorporating a turbocharger assistdevice in accordance with aspects of the present technique;

FIG. 3 is a graphical representation of a typical compressor map inaccordance with aspects of the present technique;

FIG. 4 is a flow diagram illustrating an exemplary method of operating aturbocharger in accordance with aspects of the present technique; and

FIG. 5 is a flow diagram illustrating an exemplary method of operating aturbocharger assist device based on the signals received in thecontroller in accordance with aspects of the present technique.

DETAILED DESCRIPTION

Turning now to the drawings, and referring first to FIG. 1, adiagrammatical view of exemplary functional components of aturbocharging system 10 including a turbocharger 12 is illustrated. Thearrangement illustrated in FIG. 1 includes a diesel engine 14 having adrive shaft 16 coupled to a generator or alternator 18. The alternator18 provides electric power to one or more traction motors (not shown inthe figure for clarity) for propelling a vehicle in which the engine andmotors are disposed, such as a locomotive, work vehicle, and so forth.The alternator 18 is coupled to a drive system 20, which drives thewheels 22 of the locomotive or vehicle. It should be noted that,although reference is made in the present description to a vehicle drivesystem, and more particularly to a locomotive drive system, the presenttechnique might find application outside of such environments, includingin stationary engine drive systems, such as generator sets, and soforth.

The turbo-charger 12 includes a compressor 24 and a turbine 26. Thecompressor is operable to provide a supply of compressed air to anintake manifold 28 for combustion in the diesel engine 14. The turbine26 is connected to an exhaust manifold 30 for extracting energy from theexhaust gases of the engine for rotating a turbocharger shaft 32connected to the compressor 24. The waste gases of the engine 14 flowout as exhaust gas 34 from the engine. The compressor 24 draws ambientair 36 through a filter (not illustrated in the figures for clarity) andprovides compressed air through an outlet connected to a heat exchanger38. The air is heated to an elevated temperature by compression, and ispassed through heat exchanger 38 such that the temperature of air isreduced prior to delivery into the engine 14.

Turbocharger 12 is a type of forced induction system compressing the airflowing into the engine 14. Compressing the air advantageously permitsthe engine 14 to force additional air into the cylinders of the engine14. The additional air so obtained enables more fuel being added to theengine 14, which is combined with the air for combustion. Thus, theturbocharger system effectively increases the power from each combustioncycle in the cylinder of the engine 14.

As indicated earlier, the turbocharger 12 uses the exhaust flow from thediesel engine 14 to spin the turbine 26 to achieve the compression ofthe inlet air. The turbocharger 12 is connected to the exhaust of theengine 14, and due to the high temperature of the exhaust gases of theengine 14, the turbine 26 temperature increases. The turbocharger 12 ismechanically coupled, for example, by bolting, to the exhaust manifoldof the diesel engine 14. The exhaust from the cylinders of the dieselengine 14 spins the turbine. A turbocharger shaft connects thecompressor 24 to the turbine 26. The compressor is located between theair filter (not shown in the figure) and the intake manifold 28 of theengine 14. The air pressurized by the compressor 24 is communicated tothe cylinders of the engine 14 via the intake manifold. Exhaust from thecylinders routed through the exhaust manifolds 30 passes through theturbine, causing the turbine 26 to spin. On the other end of theturbocharger shaft 32, the compressor 24 drives air into the cylindersof the engine 14.

The turbocharging system 10 also includes a controller 40. In anexemplary embodiment, the controller 40 is an electronic logiccontroller that is programmable by a manufacturer, and that may permitadditional programming by a user. The controller 40 receives varioussignals from the diesel engine 14 and the turbocharger 12 via a seriesof sensors 42-50 as illustrated in FIG. 2. Typically, the sensors 42-50include a pressure sensor 42, a temperature sensor 44, a speed sensor46, an ambient temperature sensor 48, and a mass flow rate sensor 50.However, in other embodiments of the present technique, various othersensors may be used to monitor different operating parameters of thediesel engine 14 and the turbocharger 12. Typically, the controllerincludes circuitry, such as a dedicated or multi-purpose processor,operable to generate control signals 51 in response to received signals52 indicative of the compressor operating conditions. In the embodimentillustrated, the controller 40 in turn is coupled to, or itselfincludes, a memory device storing compressor map 54, a look up table 56,or both, from which the controller 40 obtains desired operatingconditions and an operating mode of the turbocharger 12 based on thecontrol signal, independent of the speed of the diesel engine 14. Thecontrol signals generated by the controller are applied to theturbocharger assist device 60, as described below, to regulateapplication of work to, or extraction of work from, the engine 14. Thecontrol circuitry thereby controls the operation of the turbocharger 12and the diesel engine 14.

A turbocharger drive shaft 58 is coupled to a turbocharger assist device60, which is further coupled to an electrical energy source such as thealternator output, a battery 62 or multiple sets of batteries used forinitial start up of the turbocharger assist device 60. The turbochargerassist device 60 is an electric motor-generator for facilitatingindependent control of the turbocharger operation. However, other typesof devices may also be used as a turbocharger assist device 60, such ashydraulic devices. The turbocharger assist device 60 is mechanicallycoupled to the turbocharger drive shaft 58 and the turbocharger assistdevice receives an electrical control signal from controller 40. Theturbocharger assist device 60 is operable to supply work to theturbocharger drive shaft 58 (i.e. to apply torque to the shaft to driveit) or remove work from the turbocharger drive shaft 58 (i.e. to bedriven by the shaft). The operation of the turbocharger assist device ineither adding work to the turbocharger, or extracting work therefrom,defines, in the present context, two distinct operating modes.

During starting of the engine 14 in cold weather conditions, forexample, the turbocharger assist device 60 is operated as a motor (i.e.in motor mode). In this mode, torque is supplied to the turbochargerdrive shaft 58 in addition to torque supplied from the turbine 26,thereby increasing the turbocharger 12 input power, permittingcompression of additional air, and/or at higher pressures forintroduction into the cylinders of the diesel engine 14. Conversely, theturbocharger assist device 60 may be operated as a generator (i.e. ingenerator mode) during high-speed operation. When in generator mode, theturbocharger assist device 60 forms an additional load on theturbocharger drive shaft 32, which decreases the speed on theturbocharger shaft 32 and therefore decreases the power delivered to thecompressor and reduces the amount of air and/or the pressure of the airavailable for introduction into the cylinders of the diesel engine 14for combustion.

In a present implementation, a primary role of the turbocharger assistdevice 60 operating in generator mode is to avoid overspeeding and/orsurging of the compressor 24. “Surge” is a phenomenon of compressorsdiscussed below, and is generally to be avoided for proper operation. Byreducing the pressure of compressed air being provided to the dieselengine 14, the turbocharger assist device 60 functions to reduce themaximum pressure in cylinder of the diesel engine 14. By operating ingenerator mode, the turbocharger 12 speed is reduced to control maximumspeed below safe design limits while recovering useful energy in theprocess.

Referring to FIG. 2, a control circuit 64 is illustrated for operating aturbocharger 12 for a diesel engine 14, incorporating a turbochargerassist device 60. As indicated above, the controller 40 receives varioussignals 52 from the diesel engine 14 and the turbocharger 12 via aseries of sensors 42-50. The signals from these sensors are transferredto a control interface 66, and the signals are further processed in aprocessor 68. The processor 68 may perform filtering operations and makecertain computations based upon the received signals 52 and compares theprocessed signals or values with values stored in a memory circuit 70.As noted above, the memory circuit 70 may store a look up table 56containing values representative of desired operation of theturbocharger assist device 60, cylinder pressures, or other desiredoperating conditions as a function of the processed signals or computedvalues. Based upon the comparison, then, the processor 68 generatescontrol signals 51 for operation of the turbocharger assist device 60 tomaintain or reach the desired operating conditions 72, including theoperating mode of the turbocharger system in aid with the memory circuit70 and the look up table 56. The resulting control signals 51 from theprocessor 68 are applied to the control signal interface 74 forapplication to the turbocharger assist device 60, thereby regulatingoperation of the system either to drive the turbocharger drive shaft 58,thereby driving the turbocharger 12, or to extract work from theturbocharger drive shaft 58, depending upon the desired operating mode.

Turning now to FIG. 3, a graphical representation of a typicalcompressor map 76 is illustrated. The map 76 is illustrated as a seriesof traces or curves in a coordinate system defined by a corrected massflow rate axis 78 and a compressor stage pressure ratio axis 80. Thecompressor stage pressure ratio is defined as the ratio of thecompressor outlet pressure to the compressor inlet pressure. The centralline in the figure indicates an engine breathing line 82 at constantengine speed and the curve extending adjacent to the breathing lineindicates the surge line 84. Compressors are driven to higher pressureratios when any combination of the following occur; the ambienttemperature is reduced, the ambient pressure is reduced, the enginefueling is increased or the fuel injection timing is retarded. However,unstable flow may develop in the compressor, which is called surge.Ultimately, if left unchecked, such surge can damage the turbochargersystem, resulting in significant downtime and cost to repair.

As will be appreciated by those skilled in the art, such surge is theresult of flow separation in the compressor. The surge line 84represents this condition, while the breathing line 82 indicates theflow characteristic of a four-stroke engine operating at a constantspeed, which extends generally along the surge line 84. A counterpartengine breathing characteristic curve for a two-stroke engine could alsobe used. To the right of this breathing line 82 the compressor workswithout surging.

During operation of the turbocharger assist device 60 in generator mode,the additional load of the turbocharger assist device 60 decreases theturbocharger speed, thereby avoiding surge (i.e. maintaining theoperation of the turbocharger system to the right of the surge line). Onthe contrary, when the turbocharger assist device 60 functions in motormode, the turbocharger speed is increased to generate higher flow,higher compressor outlet temperature and pressure, as would be useful toenhance cold start capability.

Referring to FIG. 4, a flow diagram is illustrated for an exemplarymethod of operating a turbocharger in accordance with embodiments of thepresent technique. The process begins with monitoring at least oneoperating parameter indicative of a compressor operating condition (step88). The operating parameters may include at least one of compressorpressure ratio, manifold temperature, manifold pressure, turbochargerspeed, ambient temperature and mass flow rate of air entering theengine. As will be appreciated by those skilled in the art, thecompressor pressure ratio may be computed based on measuring the inletand outlet pressures of the compressor, such as via conventionalpressure sensors. The manifold temperature may be measured via aconventional thermocouple or resistive temperature detector disposed onor adjacent to the manifold. A conventional pressure sensor in themanifold may sense the manifold pressure. The engine and turbochargerspeed is sensed by a suitable tachometer or other rotational frequencymeasurement device, while the ambient temperature is sensed by asuitable thermocouple or resistive device. Finally, the mass flow ratemay be derived from a signal generated by a flow sensor. Certain or allof these signals may be available from sensors existing on the engine,or which may be added to the engine during manufacture or byretrofitting. Moreover, the signals may be transmitted to theturbocharger system control circuitry by dedicated conductors, or may betransmitted by appropriate network media and protocols, such as via acontrol area network (CAN) based network.

At step 90 the operating parameters selected for control of theturbocharger system are analyzed by the processing circuitry withrespect to the target operating conditions of the engine. In a presentembodiment, the operating conditions of the engine include the speed ofthe engine, the amount of air flowing in the cylinders of the engine,the temperature and the pressure of the intake manifold. The target ordesired operating conditions may be stored in the form of a look uptable. The table includes values for the desired operating parameters,and combinations of these parameters, along with settings for theturbocharger assist device. At step 92 the process controls aturbocharger assist device to maintain the desired operating conditions,particularly the conditions of the compressor. As explained above, theturbocharger assist device receives signals from the control circuitryand works either as a motor or a generator, depending upon the operatingmode.

FIG. 5 is a flow diagram illustrating an exemplary method of operating aturbocharger assist device based on the signals received in thecontroller in accordance with aspects of the present technique. Theprocess starts by sensing pressure and temperature along with otherdesired operating parameters of the diesel engine via appropriatesensors, as discussed above, and as indicated by step 94. The signalsare sensed through the sensors located in the engine as discussed above.In step 96 the pressure ratio across the compressor is computed,followed by sensing of speed of the diesel engine for determining thedesired operating conditions of the turbocharger based on the operatingparameters of the engine as represented by step 98. At step 100 the massflow rate of the air flowing into the diesel engine is estimated. Atstep 102 the processor generates a control signal in response toreceived signals and based on a comparison of the actual operationsconditions with the values of either a look-up table or a compressor map(of values tracing the surge relationships discussed above). At step 104the processor determines a desired operating condition and an operatingmode of the diesel engine. At this point, a decision is made todetermine whether the maximum desired operating pressure has beenexceeded, that is, the set pressure limit for smooth operation of theengine (step 106), and whether the operating pressure exceeds that ofthe desired state (step 108). The speed of the turbocharger may thus bereduced to avoid surge of compressor as indicated in step 110. On theother hand if the operating pressure is within the desired values orneeds to be increased (step 112), the speed of the turbocharger isincreased to generate higher flow of air for combustion in the engineand higher compressor outlet pressure as indicated in step 114.

As will be appreciated by those skilled in the art, the overall systemoffered by the present technique enables a variety of benefits over theconventional system. The turbocharger assist device coupled to thecontroller, is configured to add work to the turbocharger or subtractwork from the turbocharger based on the control signal, obtained fromthe sensors present in the diesel engine, thereby providing improvedcold start capability, active control over surge through the regulationof turbocharger speed, and elimination of turbocharger overspeed.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A controller configured to control operation of a turbocharger assistdevice in an engine for generating electric power when an excess ofenergy exists in the exhaust of the engine to subtract work from aturbocharger drive shaft.
 2. The controller of claim 1, wherein thecontroller is configured to control the operation of the turbochargerassist device based upon at least one operating parameter of the engine.3. The controller of claim 2, wherein the operating parameter comprisescompressor pressure ratio, manifold temperature, manifold pressure,turbocharger speed, ambient temperature, or mass flow rate of airentering the engine, or a combination thereof.
 4. The controller ofclaim 2, wherein the controller is configured to generate a controlsignal in response to received signals representing the at least oneoperating parameter of the engine.
 5. The controller of claim 4, whereinthe control signal is based upon surge data, engine outlet temperature,and compressor map data.
 6. The controller of claim 1, wherein theturbocharger assist device is mechanically coupled to a turbochargercomprising a compressor and a turbine.
 7. The controller of claim 6,wherein the turbocharger assist device comprises a motor-generator. 8.The controller of claim 6, wherein the controller is configured tocontrol the turbocharger assist device to add work to a turbochargerdrive shaft unless the compressor approaches a surge condition.
 9. Aturbocharger assist device configured to facilitate control of aturbocharger in an engine, wherein the turbocharger assist device isconfigured to add work to a turbocharger drive shaft or subtract workfrom the turbocharger drive shaft based upon operating parameters of theengine.
 10. The turbocharger assist device of claim 9, wherein theturbocharger assist device is coupled to a controller configured toselect a mode of operation based upon the operating parameters of theengine independent of speed of the engine.
 11. The turbocharger assistdevice of claim 10, wherein the turbocharger assist device is configuredto operate as a generator to decrease speed of the turbocharger to avoidsurge of the engine.
 12. The turbocharger assist device of claim 10,wherein the turbocharger assist device is configured to operate as amotor to increase speed of the turbocharger to generate higher flow ofair into the engine.
 13. The turbocharger assist device of claim 9,wherein the turbocharger assist device is coupled to an electricalenergy source to facilitate initial start-up of the turbocharger assistdevice.
 14. A method of controlling a turbocharger assist device coupledto a turbocharger of an engine, comprising: generating electric powerwhen an excess of energy exists in an exhaust of the engine to subtractwork from the turbocharger.
 15. The method of claim 14, comprisingoperating the turbocharger assist device as a generator to subtract workfrom a turbocharger drive shaft.
 16. The method of claim 14, comprisingoperating the turbocharger assist device as a motor to increase thespeed of the turbocharger to generate higher flow of air into theengine.
 17. The method of claim 14, comprising: receiving signalscorresponding to at least one operating parameter of a compressor of theturbocharger; generating control signals in response to the at least oneoperating parameter; and controlling the turbocharger assist device tomaintain desired operating conditions of the compressor independent ofthe engine speed.
 18. The method of claim 14, comprising controlling theturbocharger assist device to add work to a turbocharger drive shaftunless the compressor approaches a surge condition.
 19. A computerreadable medium, comprising: programming instructions configured toreceive signals representing at least one operating parameter of anengine; and programming instructions configured to generate controlsignals in response to the received signals for controlling aturbocharger assist device to generate electric power when an excess ofenergy exists in an exhaust of the engine to subtract work from aturbocharger drive shaft.
 20. The computer readable medium of claim 19,comprising programming instructions configured to operate theturbocharger assist device as a generator to decrease speed of theturbocharger to avoid surge of the engine.
 21. The computer readablemedium of claim 19, comprising programming instructions configured tooperate as a motor to increase speed of the turbocharger to generatehigher flow of air into the engine.